1. Field of the Invention
The present invention relates to the field of revolving-ladle turrets for continuous casting steel plants. More particularly, the invention relates to ladles of the type which include, on a base structure, a platform which rotates about a vertical axis, a turret member mounted on the platform, a pair of ladle-carrying arms extending out from diametrically opposed points on the turret member, and motor elements for rotation of the platform and for vertical displacement of the turret member.
2. Description of the Prior Art
Use of ladle-carrying turrets has made it possible to halve or, at least, reduce in a substantial way, the down time between two successive feeds of molten steel into the distributor of a continuous casting steel plant. In fact, while the first ladle, held by the corresponding arm in the casting position, discharges steel into the distributor, a second ladle full of molten steel can be loaded on the other arm. When the first ladle has been completely emptied, the turret with the empty ladle and the full ladle is raised, rotated 180 degrees, and then lowered to the initial height in order to recommence the simultaneous operations of discharging molten steel from the full ladle positioned over the distributor and the replacement of the empty ladle with another ladle already loaded with molten steel.
During all of these operations, the ladle-carrying arms must be held in horizontal positions.
Satisfaction of this necessity is very difficult to achieve due to the constant and evident situation in which there are unbalanced loads which act on the revolving-ladle turret.
In fact, the ladles carried at the ends of the turret arms have large, different, and quite variable weights, depending on the operating phase of the turret at any one time. This means that the straight-line action of the resultant of the weights acting on the turret not only does not coincide ever with the center-of-gravity vertical axis or the axis of rotation of the turret itself, but its distance from this axis (eccentricity) varies within a rather broad range of values, the limits of which, being both identical and contrary, are established when a full ladle is vertically above the distributor and when an empty ladle is above the distributor.
Also, for the support and vertical displacements of the turret, two identical hydraulic cylinders are generally used, symmetrically spaced about the axis of rotation of the turret. The straight-line action of the resultant of the thrusts of these cylinders coincides with the axis of rotation.
Consequently, an unbalancing torque constantly acts on the turret, determined by the resultant of the loads and by the resultant of the thrusts of the cylinders. This unbalancing torque must be effectively resisted or, better, eliminated.
For this purpose, changes have been made affecting the hydraulic cylinders for raising and support of the turret, so that the straight-line action of the resultant of their thrusts could be from time to time displaced so as to coincide at all times with the straight-line action of the resultant of the loads. Thus, devices and appliances have been devised and applied for example, to regulate appropriately the pressures of operating fluids in the cylinders, or balancing devices and/or compensating devices which, in addition to an acknowledged low reliability, have presented the inconvenience of becoming very complicated from both the structural and the functional points of view.